slant six ignition issues..shuts off wont crank

out of curiosity , where ever did you find the (hopefully) correct , one-year-only positive battery cable for your '74 ??? The correct ones were unavailable for a long time ! Guess that being a 1974-only cable , no one saw fit to make 'em ...

now , regarding the shutoff problem :
powerwagonpaul mentioned the (dreaded) Ballast Resistor , which is the problem more often than not .
Moreover , check its connectors as well . They become loose with age , and have the tendency to work themselves off ever so slightly , causing the car to do a "clean" cutoff ( i.e. , no stumbling , no theatrics ; just POOF ! Off ! ).
Also , the plastic casing which covers the connectors becomes brittle with time / age , due to engine heat and general decomposition .
The only fix that I'm aware of is to buy a new ignition harness ( ECU-to-Ballast-to-distributor ) , or to buy a whole new electronic ignition conversion kit ( specifying the 4-prong ballast ) .